The increasing demand for high SPL at low frequencies has prompted the study of nonlinearities in loudspeaker ports. At high levels, ports produce jets of air, display acoustic compression, loss and distortion, generate turbulence noise, and rectify pressure fluctuations. These phenomena are measured and analyzed. A simplified nonlinear model of a port is presented. Flared ends and gentle tapering help somewhat. The low-level linear acoustic characteristics of ports of varying cross-section are analyzed. The velocity profiles of ports are measured, and a new theory for this and the associated nearfield pressure is presented, which contradicts the usual "piston-in-a-baffle" approach.
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